Tag Archives: ground penetrating radar

Radars reveal Viking burial mounds and hundreds of mysteries in Norway

The ground was frozen and the field was covered with a fine layer of snow – ideal conditions for this type of archaeological research. Credit: Arne Anderson Stamnes, NTNU University Museum.

It’s not too often that archaeological research involves driving a four-wheeler across a frozen field, but in November 2019, that’s exactly what Arne Anderson Stamnes found himself doing. Stamnes is an archaeologist at NTNU University Museum, and he was using a ground-penetrating radar to survey the area.

Nowadays, archaeologists prefer to not dig randomly and carry out surveys such as this one to “see” the subsurface and learn where the interesting objectives are — and in the field Stamnes was looking, there was plenty of interesting stuff.

“Our findings included traces of 15 burial mounds, and one of them appears to contain a boat grave. Both the size and design of the burial mounds are typical of the period 650 to 950 CE—that is, what we call the Merovingian Period and Viking Age,” says Stamnes.

“A lot of the mounds are big. The largest burial mound has an inner dimension of 32 meters and must have been a towering presence in the landscape,” he adds.

Profiles (top) and a map (bottom) of the burial mounds. Note the circular features betraying the structure. Credit: NTNU University Museum

It was an excellent set of findings, partially aided by the environmental conditions. Ground-penetrating radar sends electromagnetic waves into the subsurface, from which they are reflected back to a receiver. Since archaeological objects have different electromagnetic properties than the surrounding soil, these waves are reflected differently, betraying the position of the objective. It’s a bit like an X-Ray of the underground. The four-wheeler Stamnes was driving towed such a radar that swept the area. The presence of snow also made the conditions excellent for this type of survey.

“The results are astonishingly good and they whet your appetite for more,” says Nordland county archaeologist Martinus A. Hauglid.

The burial mound that Stamnes mentions is one of the largest in the region, and must have belonged to an important chief. But archaeologists were even more intrigued by something else: an ever-so-small mysterious structure. Or rather, many of them.

Ditches, ditches everywhere

The survey revealed no fewer than 1257 pits of various sizes. Which begs the question: what exactly are they?

It’s hard to say for sure, also because they’re probably not one thing, but rather multiple things — from cooking pits to post holes to garbage pits. But what they do confirm is that this was a very active area.

“I’ve asked a few of my colleagues, but so far haven’t found anything similar to this find in other excavations. So it’s difficult to conclude what it might be,” Stamnes says.

“The shape and the fact that most of the ditches have a clear orientation with the short end towards the sea—probably also the dominant wind direction—make it likely that this was a type of house foundation,” he said.

This also seems to fit with the theory that the site was an old Viking power center. We already know that a powerful family lived in the area (based on the burial mounds), and there was a lot of activity (as evidenced by the pits), but more evidence is needed before any clear conclusions can be drawn.

“What we can say is that these pits are another sign that this area has been packed with human activity,” says Stamnes.

The site also showcased another interesting aspect: Eight of the burial mounds are circular in shape, while seven are oblong. Oblong burial mounds are associated with female burial, so there seems to be a pretty good gender balance in the area.

“Five of the round grave monuments have a diameter greater than 17.5 meters, where the largest measures about 32 meters. The long mounds are between 17.7 and 29 meters long,” Stamnes says.

“Building such large tombs is resource-intensive, so it’s plausible that the people buried here had great power and influence, both locally and regionally,” he says.

Hauglid is also thrilled, as is Ingrid Nøren, the manager for the New City—New Airport project in Bodø municipality.

“Bodøgård was the seat of the sheriff—and later the county governor—in the Nordland region from the beginning of the 17th century, while Bodin church nearby is a stone church from the Middle Ages. The burial ground that has now been discovered testifies that a political-religious power center has existed here since the Late Iron Age,” says Hauglid.

“A new city quarter has given us the chance to explore an area we’ve long been curious about. We can even see from aerial photos that there’s something under the ground. The findings from the investigation have yielded a long-awaited and exciting mystery,” concludes Nøren.

The findings are discussed in an online report (in Norwegian).

Archaeologists confirm location of elusive Spanish fort in Florida

Fort San Antón de Carlos was built in 1566 in the capital of the Calusa, the most powerful Native American tribe in the region. Now, archaeologists know for sure where it was located: Mound Key, Florida.

Spanish historical records named Florida’s Mound Key, the capital of the Calusa kingdom, as the site of Fort San Antón de Carlos, home of one of the earliest North American Jesuit missions. Archaeologists have now uncovered evidence of the fort on one of the island’s shell mounds. Credit: Victor Thompson

Being a modern archaeologist is a lot like working in forensics — you spend your time looking for evidence regarding people’s lives. Finding clues is one thing, but actually proving something — is another.

For instance, archaeologists and historians have long suspected that the fort, named for the Catholic patron saint of lost things, was located on Mound Key. But they were never really able to prove it, until now.

They started searching for concrete evidence in the area since 2013, in what was once Calusa territory.

“Before our work, the only information we had was from Spanish documents, which suggested that the Calusa capital was on Mound Key and that Fort San Antón de Carlos was there, too,” said William Marquardt, curator emeritus of South Florida archaeology and ethnography at the Florida Museum of Natural History.

“Archaeologists and historians had visited the site and collected pottery from the surface, but until we found physical evidence of the Calusa king’s house and the fort, we could not be absolutely certain.”

The Calusa were a Native American people of Florida’s southwest coast. They developed from archaic peoples of the Everglades region and built one of the most politically complex groups of fisher-gatherer-hunters in the world.

They were able to resist colonization for nearly 200 years, Marquardt said.

They are also considered to be the first “shell collectors,” using shells as tools, utensils, and jewelry. They would discard the fragments in enormous mounds once they were finished, and also developed massive structures to act as fish corrals to help feed their growing population. Fort San Antón de Carlos was actually built on one of these shell mounds — the only known one of this type.

The Spanish Jesuit mission living on Mount Key did not have a good relationship with the Calusa, and researchers aren’t even sure how the mission was able to survive, given that shipments from other colonies would have been scarce and infrequent.

The Spanish developed a brief alliance with the Calusa in 1569, but it quickly deteriorated, and the fort was abandoned.

“Despite being the most powerful society in South Florida, the Calusa were inexorably drawn into the broader world economic system by the Spaniards,” Marquardt said. “However, by staying true to their values and way of life, the Calusa showed a resiliency unmatched by most other Native societies in the Southeastern United States.”

Researchers from the University of Florida, the University of Georgia (UGA), and students from UGA’s archaeological field school used remote sensing and ground-penetrating radar to find the most likely hotspots for archaeological evidence, as well as to understand the overall structure of the fort (including what lies beneath the ground). Then, they carried out archaeological digs, uncovering the walls of the fort and several artifacts, including ceramic shards and beads.

The team not only confirmed the location of the fort, but also found the earliest-known North American example of “tabby” architecture — a type of concrete made from shells.

“Tabby” is made by burning shells to create lime, which is then mixed with sand, ash, water, and more broken shells. It’s a rough and primitive form of concrete, but it was successfully used at Mount Key as mortar, to stabilize posts in the walls. Tabby remained a trademark for some English colonies in the Americas, particularly in the Southern plantations — but this is the first evidence of such a structure on the continent.

“Seeing the straight walls of the fort emerge, just inches below the surface, was quite exciting to us,” Marquardt said. “Not only was this a confirmation of the location of the fort, but it shows the promise of Mound Key to shed light on a time in Florida’s—and America’s—history that is very poorly known.”

Journal Reference: Victor D. Thompson et al, Discovering San Antón de Carlos: The Sixteenth-Century Spanish Buildings and Fortifications of Mound Key, Capital of the Calusa, Historical Archaeology (2020). DOI: 10.1007/s41636-020-00236-6

Here’s why there’s almost certainly no hidden chamber in Tutankhamun’s tomb

The entire world of archaeology was electrified by recent announcements of a hidden chamber in Tutankhamun’s tomb. The story had it all – maybe even too much – false walls, hidden riches, even a mummy, Nefertiti’s mummy. But while the whole situation is still in the air, more and more doubt is being cast on the finding, and the Egyptian government seems to be suppressing important data.

Tutankhamun’s tomb, via Wikipedia.

In 2015, the then Egyptian minister of antiquities, Mamdouh Eldamaty, that he was “90% positive” of an unexpected chamber in Tutankhamun’s tomb following a Ground Penetrating Radar (GPR) survey. The data wasn’t publicly released, and to my knowledge, no one has really been able to prove or disprove it. This is where it gets sticky.

The initial optimism was sparked by a veteran Japanese specialist, Hirokatsu Watanabe. But Watanabe has refused to share his data and subject it to verification, making a very dubious statement. He said that he has customized his data so much that it would be impossible for others to understand it:

“When someone says that they want to check the data, I am so sad,” he said. But he expressed no doubts about his results: “I trust my data completely.”

But that verification is the very core of science! Being able to confirm or reproduce someone else’s data is absolutely one of the cornerstones of any important survey. Sure, GPR data is sometimes subjective and it’s often difficult to understand and interpret, but that’s definitely not an excuse.

This is how a radargram generally looks – difficult to interpret, but telling for the trained eye.

To make things even murkier, two of the most renowned scientists working with GPR in archaeological have expressed doubts about this. Dean Goodman, a California-based geophysicist carried out another scan in the same place. The survey was organised by the National Geographical Society (NGS). The data and an accompanying report was then sent to the Egyptian ministry of antiquities but was not released to the public. This raised even more doubts: if this data confirmed the original one, then why not release it?

Goodman himself has not commented on the situation, due to a non-disclosure agreement with NGS. But he was earlier quoted by the National Geographic website as saying that no hollow chamber had been found.

“If we had a void, we should have a strong reflection,” he said. “But it just doesn’t exist. Radar data can often be subjective. But at this particular site, it’s not. It’s nice at such an important site to have clear, convincing results.”

Lawrence Conyers, an anthropology professor at the University of Denver and the author of Ground-Penetrating Radar for Archaeology (the go-to book for studies like this one) also expressed his doubts:

“National Geographic came in and collected two sets of data and they used the used all the newest equipment with the right antenna. They first did a scan of a wall where they knew there was a void space behind it and used that as a model, so they knew what they were looking for. They did multiple scans of every single wall, and from what I understand, there is absolutely no indication of a void space.”

The seal to Tutankhamun’s tomb has remained untouched for thousands of years.

Looking at things in the greater perspective, everything seems to point at the absence of a hollow room. There’s simply no evidence to add up. This is a great claim, and great claims require great evidence and this is not nearly the case. To add insult to injury, the way the Egyptian ministry has handled this entire situation, shrouding it in mystery in a very non-scientific way.

There is no ‘Nazi Train’, Polish geophysicists find

This summer in Poland, two treasure hunters discovered what they believe was a WWII Nazi train filled with treasure, in a buried tunnel. Poland’s Deputy Culture Minister Piotr Zuchowski said authorities were led to the spot and that he was 99% convinced that the treasure had been located. But according to scientists Krakow’s AGH University of Science and Technology, we shouldn’t believe the hype.

Geophysicists examining the site of the alleged train.

From the very start, there was something unclear about this story. The evidence for the 99% belief in the Nazi train was based on so-called GPR (ground penetrating radar)… except the image they published wasn’t from GPR. I’m not sure what it was from, but I’ve worked with similar equipment in recent years, and have consulted with people who have done so even more – everyone agreed that it’s not GPR. That’s when the first question marks emerged about the validity of the involved science. Now, a team of researchers from Krakow University of Science and Technology came back to look in more detail – using magnetic and gravity measurements.

While ground penetrating radar works by emitting an electromagnetic pulse and recording its return, gravity and magnetic measurements measure existing fields. Gravity is suited for detecting large structures and underground voids – as they create a high enough contrast. Meanwhile, magnetic measurements are highly susceptible to metals, so if there were a treasure or some load of guns there, you’d definitely expect to see it. Even if there was a train, it would definitely have lots of metal you would see through magnetics… except you don’t. The team from AGH University was convinced there was no Nazi train.

“There may be a tunnel,” Janusz Madej, leader of the team, said at a press conference. “But there is no train.”

This seems to translate into “we found some kind of buried structure, but there was no indication of anything metallic.” Piotr Koper and Andreas Richter, the two men who claimed to have located the train in Walbrzych, Poland, still stand by their discovery, but the science seems to claim otherwise.

“There can’t be a mistake,” Koper said Tuesday, according to the newspaper.

Investigations will likely continue in the future, and using more geophysical methods in conjunction with each other could fill in the gaps, because there is always uncertainty with any remote detection method. Drills will also be carried on to directly see what’s down there.

Between 1943 and 1945, the Nazis forced prisoners of war to dig more than 9km of tunnels near Walbrzych, probably to be used as factories. However, popular folklore believes the Nazis wanted to establish a secret command centre linked by tunnels to the Owl Mountains south-east of the city. People have been chasing the legend of the train for decades, and apparently, they’ll have to keep looking.

Chinese Lunar Rover Reveals Secrets from The Dark Side of the Moon

The Moon’s geologic past was much more interesting and active than previously thought, results from the Chinese lunar rover indicate. The Yutu moon rover found evidence of at least nine distinct rock layers deep beneath its wheels, something which seems to indicate a more complex and active setting.

lunar rover yutu

Image via CCTV.

“We have for the first time detected multiple subsurface layers (on the moon),” said lead author Xiao Long, professor of the China University of Geosciences in Wuhan, attributing these layers to ancient lava flows and the weathering of rocks and boulders into regolith, or loose layers of dust, over the past 3.3 billion years or so.

The Yutu mission was initially considered a failure, after the rover stopped only weeks after it was launched due to technical difficulties; it only covered 114 meters. But analysis of the data it gathered in the short timeframe is starting to reveal unknown features of the satellite. In a statement, Xiao Long said:

“Two things are most interesting. One is [that] more volcanic events have been defined in the late volcanism history of the moon. Another is the lunar mare [volcanic plain] area is not only composed of basaltic lavas, but also explosive eruption-formed pyroclastic rocks. The latter finding may shed light on … the volatile contents in the lunar mantle.”

Image via Xinhua.

The rover was equipped with a Lunar Penetrating Radar (LPR) capable of probing 1,300 feet (400 meters) beneath the lunar surface. The technology was basically a Ground Penetrating Radar, something used on Earth for decades to probe the near surface (and in some cases, even going deeper). The LPR sends short radar pulses that travel in the underground; as they encounter a different layer, a part of the pulse’s energy is sent back to the receiver, while another part continues its journey deeper. The receiver’s antenna notes the wave shape, along with the time it took for the wave to return, thus enabling scientists to “visualize” the different underground layers.

Probably the most interesting discovery is a layer at depths of 140 meters to 240 meters, said Xiao, who is also professor of Macau University of Science and Technology.

“We think this layer is probably pyroclastic rocks which formed during the course of volcanic eruptions,” Xiao told Xinhua via email. “It reveals the diversity of volcanic activity, but what’s more important is that it shows there are plenty of volatile contents inside the moon.”

Pyroclastic rocks are rocks composed solely or primarily of volcanic materials, while volatiles are the group of chemical elements and compounds with low boiling points that are typically found with a planet’s or moon’s crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, methane and sulfur dioxide.

Yutu (whose name means “jade rabbit”) is part of China’s Chang’e 3 moon mission. Chang’e 3 delivered Yutu and a stationary lander to the lunar surface on Dec. 14, 2013 – the first soft lunar landing since 1976. Yutu still cannot move the solar panels back to the insulating position during the lunar nights, exposing the internals to the nightly cold and continuous degradation. However, despite not being able to move and function properly, the Jade Rabbit is still sending valuable information back to Earth.

“Overall, we have already had a general scientific understanding of the moon thanks to these lunar missions. But if we want to have a comprehensive understanding of moon’s geological structure, material composition and formation, as well as its evolution, a large number of exploration events are still needed. Meanwhile, effective international cooperation is a must considering the high cost of these activities,” Xiao stressed.

The rover has a dedicated, although not official, Weibo account (Jade Rabbit Lunar Rover) with over 600,000 followers, sometimes posting humorous status updates.

Mega canyon discovered under Greenland ice sheet

Geophysical data from Greenland have revealed the existence of a canyon comparable in size with the Grand Canyon beneath the ice sheet.

The canyon has the characteristics of a winding river channel and is over 750 km long and it is often as deep as 800 m. This immense feature is thought to predate humanity – it came to be several million years before the Antarctic ice sheet was developed.

“One might assume that the landscape of the Earth has been fully explored and mapped,” said Jonathan Bamber, professor of physical geography at the University of Bristol in the United Kingdom, and lead author of the study. “Our research shows there’s still a lot left to discover.”

Scientists used thousands of kilometers of airborne radar data collected by NASA and researchers from the United Kingdom and Germany over several decades, and managed to puzzle together the main characteristics of the Greenland canyon. They found that the geologic feature starts from almost the center of the island and ends beneath the Petermann Glacier fjord in northern Greenland.

At certain wavelengths, radar waves can travel through the ice, but bounce off the solid rock underneath. This enables us to map the depth of the canyon – the longer it takes for the wave to return, the deeper the canyon is.

“Two things helped lead to this discovery,” said Michael Studinger, IceBridge project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It was the enormous amount of data collected by IceBridge and the work of combining it with other datasets into a Greenland-wide compilation of all existing data that makes this feature appear in front of our eyes.”

Geologists believe the canyon plays an important role in transporting sub-glacial meltwater from the interior of Greenland to the edge of the ice sheet into the ocean. Existing evidence (this canyon included) suggests that before the ice sheet existed, some 4 million years ago, the canyon hosted an extensive river system which flowed from the interior to the coast.

“It is quite remarkable that a channel the size of the Grand Canyon is discovered in the 21st century below the Greenland ice sheet,” said Studinger. “It shows how little we still know about the bedrock below large continental ice sheets.”

For more information about IceBridge, the operation which led to this discovery, check out their website. The IceBridge campaign will return to Greenland in March 2014 to gather more data and develop a more conclusive picture of the subglacial features in Greenland.


When CSI and geophysics meet

We probably all know (especially thanks to the abundancy of TV series) what Crime Scene Investigators (CSI) are. Probably not so many people know exactly what geophysics is. As the name says it (geo=earth), geophysics studies the phyisical properties of the Earth, such as gravity, electromagnetism, plate tectonics, and extremely numerous other ones; it is commonly used for prospecting oil and mineral resources, as well as for environmental hazards, and even in archaeology. At a first glance, these two fields would have absolutely nothing to do with one another, but that’s not true at all.

Researcher Dr Jamie Pringle of Keele University knows how much geophysics can help CSI, by finding objects located underground or underwater, such as a murder weapon, a body, or even smaller clues. About 25% of all murder victims are dumped underwater, and 15% of them are buried, so that makes almost half of all murder victims. Some times, dogs or metal detectors are all that’s needed, but in well thought crimes, in which the killer has time to bury deeper, that’s just not good enough.

‘A lot of clandestine burials are done in a panic and those are easy to find,’ says Pringle. When dealing with more well thought out murders, it can be much more difficult, and this is where geophysics can come to the rescue.

So, in order to test the different ways of detection, a few bodies had to be buried; thankfully, it wasn’t about humans, but pig bodies, which(even though most people don’t like to admit) have a lot in common with us  – at least physically. In order to ‘see’ what’s underground, when dealing with this kind of cases, the most common method is called Ground Penetrating Radar (GPR). Initially developed to locate mines, this technology is used now also to find avalanche victims, microfissures in constructions, and small archaeological objects. The GPR got its first big break in 1994, when it was successfully used to locate the victims of serial killers Fred and Rose West.

GPR works by sending EM waves to the ground and timing how much it takes them to return. The travel time is dependant on the material through which it passes, so for example if you have a body buried somewhere, the radar will understand that the travel time for the body is different than that of the ground, and thus figure out that there is something different in there. Of course, this means that the GPR also has its limitations; first of all, it can only figure out contrasts, so if what is buried is pretty similar to the surrounding environment, the odds of finding it are minimum.

‘If you’re looking for a gun in a metal scrap yard, you’re not going to find it,’ comments Pringle.

The GPR machine is very sensitive, and the rates of success also depend on several other factors, such as soil type, how long it has been buried, and whether the body is clothed or not – a “dressed” pig is easier to find than a naked pig. Also, rough terrain is a disadvantage. This, and the fact that it is quite expensive, contribute to the GPR being relatively uncommon for the police.

‘I think the technique’s fairly well known, it’s just that it’s sometimes incorrectly applied,’ says Pringle.

Luckily, geophysicists are an inventive and smart bunch, so they use it combined with another methods, most commonly with electricity: they test the electrical resistivity, the soil’s ability to resist a passing electrical current.

‘As you decompose, your tissue and blood will mix with the soil water and give a very conductive leachate,’ explains Pringle. As a result, an electric current will flow more easily through a patch of ground where a body is buried, allowing geophysicists to spot potential graves.